An RSA algorithm for public-key cryptography has been widely used since it was introduced by R. L. Rivest, A. Shamir, and L. Adleman in late 1970s. The RSA algorithm involves a public key and a private key. The public key can be known to everyone and then used for encrypting messages. The messages encrypted with the public key can only be decrypted using the private key.
One of the applications of the RSA algorithm is a digital signature scheme. The digital signature scheme typically involves three algorithms: a key generation algorithm, a signing algorithm, and a signature verifying algorithm. First, according to the key generation algorithm, a signer selects a private key and a corresponding public key. Second, according to the signing algorithm, the signer produces a signature, given a message and the private key. Lastly, according to the signature verifying algorithm, a verifier either accepts or rejects the message's claim to authenticity, given the message, the public key and the signature.